This faculty of clustering together is still better exemplified in the genus Uvella, (1, jig. 1,) which somewhat resembles a trans parent mulberry rolling itself about at will, whence the name " grape rnonad," which these animalcules bear. In Polytoma (2, fig. 1) this clustered appearance is due to the fact that the original animalcule is continually dividing into a greater and still greater number, which, at last breaking loose from each other, become solitary and independent.
Some animalcules of this family, as Chilo monas destruens, live in the interior of dead Rotifers and other minute beings, in which locality they seem to revel luxuriously ; whilst others, as Bodo, (4, fig. 1,) are met with in the intestinal canal of many living animals,* from the fly and the earth-worm up to fishes and even men. One species (B. ranarum) seems particularly partial to the intestines of Frogs, in the contents of which it is usually found. Many species of this genus are fur nished with long tails, by the aid of which they are bound together in bunches of very beautiful appearance, as represented in the figure.
In the Cryptomonads, (5, fig. 1,) which seem to be merely Monads invested with a shell, the proboscis is of a similar character; but these animalcules are never found asso ciated in bunches.
Perhaps few more beautiful objects exist in nature than the next group of animalcules belonging to the Monadine type. These are the Volvocinidee, embracing several genera composed of numerous Monads, associated together and connected by a common envelope, which constitutes a kind of compound poly pary or monadary, as it has been recently called, through which the proboscides of the component Monads are exserted.
In Gonium, (7, 8, fig-. 1,) one of the simplest forms belonging to this family, the common body resembles a minute square shaped flattened tablet, so transparent as to be detected with great difficulty, in which the green Monads are set like the gems in the breastplate of the Jewish high-priest, from which circumstance one species, G. pectorale, has been named.
The organisation of Gonium pectorale, as far as it has been made out, seems to be as follows :—The mantle or proper covering of each individual animalcule, which can only be properly examined after the division of the little tablet, is neither four-cornered nor table like, but pretty nearly mund, and in the form of a lacerna, which the animalcules can quit and renew ag,ain at intervals. The table-like investment of the compound body is produced by regularly repeated spontaneous fissure in the longitudinal, but not in the transverse di rection, which is in fact only an imperfect division into single tablets. In a little tablet of
this kind all the animalcules of which it is composed appear to be connected to each other by riband-like prolongations.
It is only in Gonium pectorale that locomo tive organs have been satisfactorily detected, presenting themselves under the usual form of two thread-like proboscides, appended to the mouth of each individual Monad entering into its composition. These are seen to be in con stant motion, so as to have the appearance of cilia.
Each individual animalcule inclosed in the common envelope of the compound being ap pears, moreover, to possess a distinct nutritive apparatus, consisting of transparent vesicles visible among the green matter that fills its interior; but these have not yet been observed to fill themselves with colouring matter. Eh renberg likewise supposes that each of the component animalcules of the Gonium contains the essential parts of a double sexual system, regarding the green-coloured particles in the body as eggs, and an opaque spot and con tractile bladder, which is occasionally discern ible, as the male apparatus; but these parts will be more paiticularly described hereafter.
The most beautiful animalcules belonging to the Volvocinid are the Volvoces, from which the family derives its name. These, which may readily be procured in summer time, are sufficiently large to be visible to the naked eye, and when examined with a microscope, even of very humble power, present a spectacle of indescribable beauty ; turning continually upon their axes, and revolving majestically through the drop of water that forms their space, they have the appearance of so many microscopic vvorlds (fig. 2). The parietes of these elegant spheres are thin and pellucent as the walls of an air bubble ; and in theirinterior, which is obviously fluid, may at times be seen rotating on their axes a second generation moving freely in the interior of their parent, and only awaiting the the Volvox, and which he had previously re garded as the bulbous roots of locomotive cilia, he perceived in each corpuscle a bright red point, and moreover discerned that instead of its being a cilium which was appended thereto, it was a whip-like moveable proboscis exactly similar to that of the Monads described above ; and further observation convinced him that every green point was in reality a distinctly organised Monad, possessing mouth, eye, sto machs, generative apparatus, and, in fact, all the viscera attributed by Ehrenberg to the free Monadinidm, and that the Volvox was entirely made up of an association of similar individuals (fig. 3).